The present disclosure relates to a storage unit provided with a storage device that holds information with use of a variable resistance property, and a method of driving such a storage unit.
For information apparatuses such as computers, dynamic random access memories (DRAMs) with a high-speed operation and a high density have been widely used as random access memories. Unfortunately, DRAMs involve increased manufacturing costs, because their manufacturing process is more complex than that of typical large scale integrated circuits (LSIs) in a logic circuit or signal processing circuit for use in an electronic apparatus. Moreover, since DRAMs are volatile memories in which information is lost when the power is switched off, they have to undergo frequent refresh operations. Each refresh operation includes: reading written information (data) from a DRAM: amplifying the information again; and rewriting the information to the DRAM.
Meanwhile, in recent years, nonvolatile memories have been increasingly used, in which information is not lost even when the power is switched off. The use of nonvolatile memories is expected to reduce the power consumption, because no refresh operation is necessary. Various types of storage devices to be used with nonvolatile memories have been developed so far. One example is a so-called resistance change type of storage device, which holds information with use of a variable resistance property. Certain resistance change types of storage devices have a relatively simple structure, and are advantageous to overcome the limitation of the microfabrication. For example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-536840 discloses a resistance change type of storage device having a structure in which an ion conductor containing a predetermined metal is sandwiched between two electrodes. In addition, Japanese Unexamined Patent Application Publication No. 2005-197634 discloses a resistance change type of storage device that is capable of stably retaining information over an extended period or under the condition of a high-temperature environment.